Engineers are constantly seeking new strategies of reducing undesirable emissions, such as NOx and particulate matter including hydrocarbons and soot. One method of reducing emissions is to control the injection strategy of fuel into a combustion chamber. It has been found that varying the timing, the number and fuel amount of the injection(s) can alter the amount of undesirable emissions being produced by combustion.
Although controlling the injection strategy of fuel into the combustion chamber can reduce undesirable emissions, an injection strategy found to reduce concentrations of one undesirable emission may result in a relatively higher concentration of another undesirable emission. For instance, a fuel injection relatively early in a compression stroke, such as 60° before top dead center, may result in low NOx emissions, but may create relatively high hydrocarbon emissions. An injection relatively late in the compression stroke, such as near top dead center, may result in low hydrocarbon emissions, but relatively high NOx emissions.
Similarly, at different engine loads, the engine has different demands and produces varying concentrations of different undesirable emissions. For instance, at low loads, the lesser amount of fuel typically injected into the combustion chamber inherently produces lower hydrocarbon amounts in the engine exhaust. At mid-low engine loads, the injection strategy may be designed to maintain low hydrocarbon emissions. However, as engine load increases, the more the injection strategy must be designed to meet the power demand on the engine. For instance, an injection strategy, such as an early injection, that produces low NOx concentrations at a low engine load may not provide sufficient power output at high engine loads.
Further, the more control over the timing and amount of fuel injections, the greater the ability to reduce undesirable emissions. Because conventional fuel injectors include only one set of nozzle outlets, the injectors can inject fuel in only one spray pattern. Because conventional fuel injectors inject fuel in a spray pattern with a relatively large angle, with respect to a centerline of the combustion chamber, fuel injected when an engine piston is relatively low in the cylinder can make contact with the cylinder walls. This can lead to fuel-to-oil dilution and significant mechanical problems, such as piston seizure due to lubrication losses. Thus, the timing and amount of fuel that can be injected by a conventional fuel injector is limited. U.S. Pat. No. 6,725,838 to Shafer et al. sets forth one example of a fuel injector capable of injecting fuel at both a narrow, or wide spray angle via separate sets of fuel injection orifices. While Shafer et al. discuss various designs and operating strategies, there remains room for improvement.
The present disclosure is directed at overcoming one or more of the problems set forth above.